An orthopedic cast according to a relatively recently introduced practice is formed by first placing a protective sleeve over the body member and then wrapping the protective sleeve with a padding to provide cushioning of the body member. A roll of flexible, warp-knitted, fiberglass fabric webbing impregnated with a water-activated casting material is wet with water, unrolled and wrapped around the body member. The water activated system sets and hardens and thereby forms the cast.
Fiberglass yarns used in making orthopedic casting bandages incorporate some type of finish or binder, typically a starch size, which holds the individual fibers together and facilitates both processing in manufacture and knitting. When the fabric is heat cleaned at a typical temperature cycle up to 750.degree. F. to remove the starch prior to being impregnated with the water-activated casting material, the fabric tends to set and lose some of its desired stretch character in the final impregnated bandage product. U.S. Pat. No. 3,654,046 provides background information on heat cleaning and its effect.
A more recent practice has been to utilize the bandage fabric without heat cleaning and to impregnate the fabric with a water-activated resin impregnated casting material compatible with the presence of one and one-half to two percent by weight starch finish in the yarn. It has been found possible to package a roll of such fabric without fear of hardening in the typical air and liquid impervious sealed foil pouch used to hold the bandage preparatory to use. A two-bar, warp knit fabric of acceptable stretch character made entirely of non-heat cleaned fiberglass fabric with a compatible water-activated resin impregnated casting material was previously developed and has been successfully marketed under the trademark K-Cast by the Kirschner Medical Corporation of Timonium, Md.
Warp knit casting bandage fabrics, as with many other knit fabrics, tend to unravel and fray particularly at the leading edge. This is illustrated in FIG. 1 showing the prior art two-bar, all-fiberglass, warp knit casting bandage construction having this undesired characteristic. While having a somewhat lesser tendency to unravel and fray, the trailing edge of such a bandage also has a tendency to unravel and fray as also illustrated in FIG. 1. Since casting bandage fabric is knit in a long length and then cut to the length of the individual casting bandage, the unravelling and fraying problem is severe on both the leading and trailing ends of each length of casting bandage. While an all-polyester, warp knit casting bandage has been employed with less of an unraveling and fraying problem, such a casting bandage lacks the desirable characteristics of a fiberglass yarn-based casting bandage.
Heat-cleaned, fiberglass casting bandage fabric, while introducing an undesirable stretch characteristic, nevertheless has tended to provide a relatively tight fabric having relatively less tendency to unravel and fray. On the other hand, the two-bar, fiberglass, warp-knitted, non-heat cleaned casting bandage fabric while having a desirable stretch characteristic has introduced the undesirable tendency to unravel and fray easily at both ends but particularly at the leading end. U.S. Pat. No. 4,609,578 discusses the fraying problem and emphasizes the importance to the trade of finding a satisfactory solution. However, it is noted that the process set forth in the patent to reduce unravelling and fraying requires heating the entire fabric to 1000.degree. F. and exposure to such high heat, while well below the melting point of fiberglass yarns which is substantially above 1000 F., is nevertheless known to increase stiffness and cause embrittlement of the fabric.
The present invention provides both a unique casting bandage construction and yarn bonding technique for eliminating the unraveling and fraying problem. Therefore, reference is next made to prior art bonding practices with knitted fabrics.
Heat bonding of thermoplastic threads on edge portions of warp-knitted fabric is taught in U.S. Pat. Nos. 2,578,889 and 4,320,634. U.S. Pat. No. 2,578,889 teaches adhering together those threads forming warp knit fabric edges to prevent curling during processing and before the edges are trimmed. Such process prevents curling but produces an inherently stiff fabric which is not desirable for use as a casting bandage. U.S. Pat. No. 4,320,634 relates to a relatively stiff warp knit hem tape with thermoplastic yarns in the edges but whose characteristics are not suited to use as a casting bandage. U.S. Pat. No. 2,594,521 teaches heating an entire flatbed knitted fabric to bond the stitches together and which produces an overall stiff fabric unsuited for use as a casting bandage. U.S. Pat. Nos. 2,811,029 and 3,611,755 teach circular knit hosiery fabric in which a thermoplastic yarn is introduced into a selected portion of the fabric, then heated to bond together the stitches formed from another yarn of higher melting temperature to prevent runs. Such non-run hosiery fabric however is not suitable for use as a casting bandage because of the lack of selvages, because of lack of sufficient body in the fabric and because of the stiffness introduced. U.S. Pat. No. 3,142,109 teaches use of a heat sensitive plasticizer to bond fabric yarns together. While not illustrated in this last-mentioned patent, reference is made to warp knit fabric used for ordinary bandages. However, since the entire fabric is heat bonded, it would be expected that a substantially stiff fabric unsuited to use as a casting bandage would result.
The desired characteristics of a casting bandage are further discussed in U.S. Pat. Nos. 3,686,725; 3,787,272; 3,793,686; 3,882,857; and 4,502,479. Even though the desired characteristics of the conventional warp knit casting bandage fabric knit of fiberglass yarns have been identified, the problem of unraveling and fraying of the cut ends of the fabric has presented a recurring problem to the industry. While the prior art has also illustrated as described above warp knit fabric with edges formed by threads bonded together using thermoplastic yarn as well as warp knit fabric bonded throughout the fabric, the prior art has not provided a commercially-acceptable, non-unraveling, non-fraying, water-activated, resin-impregnated, flexible and body-conformable warp knit casting bandage using non-heat cleaned fiberglass fabric as the base fabric.